The primary objective of this project is to determine the factors governing the reliability with which weak signals are transmitted from receptors to bipolar cells across an inherently noisy synapse. More immediate goals include: 1) To understand the neural circuit by which the bipolar cell receives its input. 2) To understand the ionic mechanisms underlying the bipolar cell's light response. 3) To understand the factors governing the release of transmitter from the receptors. These questions will be studied using intracellular recording techniques in conjunction with spatially defined optical stimuli. An isolated retina preparation will be perfused with solutions of known ionic composition. An analysis of synaptic voltage noise will be carried out as a means of studying synaptic transmitter release. In addition, electron-microscopic study of bipolar cells, stained iontophoretically, will determined whether the functional characteristics of receptor-bipolar cell synapses are correlated with a characteristic morphology.